The lubricant additive industry generally uses alkyl phenols (e.g., tetrapropenyl phenol, TPP) to prepare detergents comprising sulfurized metal alkyl phenate. Sulfurized metal alkyl phenates have been used as additives in lubricating oils for marine, automotive, railroad and air-cooled engines for more than forty years. Generally, there may be some unreacted alkyl phenols such as tetrapropenyl phenol (TPP) present in the sulfurized metal alkyl phenate as well as in lubricating oils containing one or more of the sulfurized metal alkyl phenates.
A recent reproductive toxicity study in rats sponsored by the Petroleum Additives Panel of the American Chemistry Council shows that free or unreacted TPP may cause adverse effects on male and female reproductive organs. Further, it is believed that TPP may be corrosive or irritating to the skin.
Generally, a sulfurized metal alkyl phenate can be prepared by (1) neutralizing an alkyl phenol (e.g., TPP) with a base (e.g., calcium hydroxide) in the presence of a glycol promoter to form an metal alkyl phenate (e.g., alkyl calcium phenate); (2) sulfurizing the metal alkyl phenate with sulfur to crosslink the aromatic rings of the metal alkyl phenate to form a sulfurized metal alkyl phenate; and (3) overbasing the crosslinked sulfurized metal alkyl phenate with carbon dioxide to increase the total base number (TBN) of the product. However, some sulfurized metal alkyl phenates prepared by such methods may contain a high level of unreacted alkyl phenol (e.g., TPP).
To reduce any potential health risks to customers and to avoid potential regulatory issues, there is a need to reduce the amount of free alkyl phenol in the sulfurized metal alkyl phenates. Furthermore, there is a need for new lubricating oil detergents with a low free alkyl phenol content. Furthermore there is a need for new lubricating oil detergents having a low sulfur content.